The present invention pertains to a robust thermal barrier suitable for use as a structural member or as a coating. In particular, a first configuration may be a self-supporting or load-bearing wall of a structure, e.g., a room in a ship. A second configuration may be a surface coating for energy conservation or reducing the infrared (IR) signature of an object.
Today""s navies are operating with reduced crews that are being asked to respond to emergencies with the same efficiency as the larger crews of the past. This impacts the ability to protect resources, especially given that some of the crew has been replaced with additional high explosive ordnance, increasing the volume susceptible to hostile action or catastrophic accidents. Additionally, new and retrofit shipbuilding is being scrutinized for implementation of cost saving initiatives, to include impact on life cycle costs. A solution that reduces operational risk as well as capital investment and maintenance expense is needed. In the recent past, pumice has been used as part of a technological solution to enhance the U.S. Navy""s mission readiness by providing an effective barrier against sympathetic detonation of weapons stored in magazines and transport containers. The natural characteristics of a pumice-based barrier include both shock absorption and thermal insulation as discussed in more detail below. Of course, other materials, natural or man-made, with properties similar to pumice may be substituted.
Pumice used for construction often is mixed with Portland cement, water, and other additives to provide desirable attributes of weatherproofing, appearance, and water and wear resistance. See U.S. Pat. No. 5,759,260, Method for Using Lightweight Concrete for Producing a Combination Therefrom and a Combination Produced Thereby, issued to Groh, Jun. 2, 1998. A common use of lightweight materials, such as pumice, is for production of pre-formed panels or other structures. See U.S. Pat. No. 5,440,846 (panel with insulated core), Construction for Building Panels and Other Building Components, issued to Record, Aug. 15, 1995; U.S. Pat. No. 4,567,705 (panel for fire protection), Fire Protection Arrangement and Method for Positioning Same, issued to Carlson, Feb. 4, 1986; and U.S. Pat. No. 4,259,824 (panel with some inherent insulative property), Precast Concrete Modular Building Panel, issued to Lopez, Apr. 7, 1981. Another use of lightweight materials is for smaller building components such as construction blocks. See U.S. Pat. No. 4,641,470, Construction Element, issued to Baumberger, Feb. 10, 1987 in which a block of lightweight materials, having cavities cast therein, has the cavities filled, in a second step, with insulating materials.
Applying commonly used construction materials in formulation of the material""s mixture and the resultant structure assures local availability and an inherent confidence in the product since the builder is familiar with the performance of known materials. See U.S. Pat. No. 5,860,268, Light-Weight Concrete Door, issued to McWilliams, Jan. 19, 1999 in which a metal frame, wire mesh, hinges, and wooden molds, all common construction material, are combined with a concrete mix and a novel air entrainment admixture. . See U.S. Pat. No. 5,875,607, Low-Cost Exterior Insulation Process and Structure, issued to Vohra, Mar. 2, 1999, in which bags of insulating material that may contain pumice as part of the mix, are placed against existing exterior walls, connected to the wall, covered with stucco wire, and stuccoed for a finished surface.
Should one wish to particularly exploit a particular characteristic of material having the properties of pumice as used in a building material, one needs to carefully select a binder, and method of application of the binder, in order to optimize that characteristic. One such desirable characteristic of a pumice-like material is its resistance to conducting heat, in particular, high heat.
When exploiting a number of desirable characteristics of pumice, however, no one characteristic is likely to be optimized. See U.S. Pat. No. 4,231,884, Water Retardant Insulation Composition Comprising Treated Low Density Granular Mineral Material and Finely Divided Limestone or Similar Carbonate or Silicate Mineral Particles and Method for Using Same, issued to Dorius, Nov. 4, 1980. The ""884 patent provides an insulative composition that is also a water retardant, a corrosion preventative, and capable of use in building a load-bearing wall. To accomplish all of these objectives, certain additional coatings are provided for the lightweight inorganic material. As well, the physical composition of the mixture is adjusted to accommodate each objective. No one objective is being optimized in the mixture.
Pumice has been used for the fabrication of refractory materials. See U.S. Pat. No. 5,228,914), Pumice Containing Composition, issued to Miceli, Jul. 20, 1993 (a mixture of crushed pumice, calcium aluminate, glass fibers and water for use in ovens, heaters, and other high-temperature applications). For this application, the precise makeup of the mixture must be followed to attain the refractory material, an important ingredient being calcium aluminate.
Pumice, in combination with a binder of cement, such as PORTLAND cement, and water, and other optional ingredients such as volcanic ash, scoria, vermiculite, mineral wool and even kerosene, was used to create an insulative thermal barrier. See U.S. Pat. No. 4,803,107, Light Weight Thermal Insulation Material Product and Process, issued to Knowles, Feb. 7, 1989. Again, the product resultant from the above process was intended to address a number of objectives such as water retardation, the xe2x80x9cR-factorxe2x80x9d of the product for use in residences, and structural strength. Further, pumice comprised less than twenty percent of the mixture so that objectives other that fire retardation could be addressed by the product.
Aggregates of inorganics have also been an ingredient in coatings that may be applied by spraying, brushing, rolling, troweling, or using generally accepted stuccoing methods. See U.S. Pat. No. 5,556,578, Aggregate Containing Hydration Water in Spray Applied Fireproofing, issued to Bemeburg et al, Sep. 17, 1996 and U.S. Pat. No. 5,034,160, Sprayable Fireproofing Composition, issued to Kindt et al, Jul. 23, 1991. The ""578 patent describes a slurry for spraying on structural components, such as steel beams, to provide a flame-retardant surface. The slurry comprises a cementitious binder, such as PORTLAND cement and water, and a hard aggregate having hydration water, such as bauxite, together with optional additives, such as shredded polystyrene aggregate and starches, to aid application. The ""160 patent describes a multi-element composition suitable for use as a sprayed-on coating. The composition includes a cementitious binder such as PORTLAND cement and water, a porous aggregate that could include pumice, a fibrous material, an air-entraining agent, and a rheopectic (a fluid mixture that, when subjected to a shear force, increases in viscosity) agent. Both the ""578 patent and the ""160 patent are directed to a solution of the problem of pumping the mixture over large distances, e.g., the upper floors of high-rise buildings and, as such, are addressing a number of competing objectives.
Optimizing the use of pumice-like material for construction may key on the attributes of strength, cost, appearance, and ease of application with little or no attention paid to thermal conduction. A carefully crafted mixture, optimized for performance as a thermal barrier, may not meet one or more of the above requirements for general construction. In fact, this xe2x80x9ccarefully craftedxe2x80x9d mixture may have been considered and subsequently rejected because it did not meet the builder""s more immediate objectives.
As noted above, pumice has been used as an ingredient in construction materials where a lightweight substitute for concrete or adobe has been called out in specifications. It has also been used for packing around explosives to preclude sympathetic detonation of a neighboring explosive should one of a package be detonated. See U.S. Pat. No. 5,158,173, Weapons Storage Container to Prevent Sympathetic Detonation of Adjacent Weapons, issued to Halsey et al, Oct. 27, 1992, incorporated herein by reference in particular to the shock and blast resistance of pumice barriers, and U.S. Pat. No. 5,160,468, Method for Preparing a Storage Container for Explosive Rounds, issued to Halsey et al, Nov. 3, 1992, incorporated herein by reference in particular to the shock and blast resistance of pumice barriers. Further, there exist any number of methods to provide a separate insulation barrier, examples of which are the ""607 patent and the ""884 patent.
Combining pumice-like material with a suitable binder for pouring into forms for making, in a single process, a thermal barrier with structural integrity has not been perfected prior to this invention.
A preferred embodiment of the present invention comprises a mixture of pumice or pumice-like particles and a binder, whereupon said mixture is either poured into a form, with optional reinforcement, for fabricating a structure or applied as a coating. The binder can be any of a number of suitable admixtures, including, but not limited to, a Portland cement; a plaster; an epoxy; a resin, including a polyester or epoxy resin; and a polymer binder, or a combination of the above.
In one preferred embodiment, the pumice or pumice-like particles are of a size between xc2xcxe2x80x3 (0.63 cm) and xe2x85x9cxe2x80x3 (0.94 cm) and the epoxy is a commercially available two-part epoxy. This mixture is poured into forms much like concrete forms but not requiring the same strength since the material is much lighter than concrete. It can be poured into forms positioned horizontally, vertically, or any angle in between. It can also be poured into forms enclosing non-traditional shapes, such as ogives, truncated pyramids, cylinders, and irregular shapes to enclose odd-shaped devices such as gun turrets or boilers with accompanying ductwork and piping. Because of the relatively low density of the material, lightweight removable partitions or panels can be formed from it, facilitating modification or maintenance work.
In a second preferred embodiment, a mixture of pumice or pumice-like particles and binder is used to coat heat emitting devices in order to conserve heat or reduce the infrared signature of the device, or both. This coating may serve as a replacement for asbestos barriers now subject to strict environmental regulations.
Although the same size particles may be used in the coating mixture as for forming a structural member, ease of application may call for the use of smaller particles on the order of xe2x85x9xe2x80x3 or smaller. However, it is beneficial to maintain a minimum particle size. The insulation value of this thermal barrier depends on formation of air spaces, or voids, between the particles. Since the particles do not pack tightly, one surface mating exactly with another, these voids are an inherent consequence of forming such a coating. This coating may be applied to any surface, including those of irregular conformation and texture. Optionally, a first adhesive layer may be needed to insure proper adhesion of the mixture to the surface. Material to coat such an adhesive layer is selected based on the materials content and conformation of the surface to be coated.
Advantages of preferred embodiments of the present invention, include:
dual use fabrication as a structural member and a thermal barrier;
high weight percent of naturally heat resistant material;
lightweight, high strength substitute for concrete;
able to be formed into any shape;
increased fire resistance, lowering operating costs and risks;
reduced fire insurance rates;
simplified design of alternate configurations;
inexpensive fabrication;
reduced system complexity requiring a single member to serve multiple functions;
environmentally friendly, using natural materials and suitable for use with
the most environmentally compliant binders;
able to be sprayed, brushed, rolled, troweled, or applied as a stucco to any surface;
impervious to sporadic water damage;
reduced system capital costs;
increased operational readiness;
low maintenance costs;
increased flexibility;
high reliability;
particularly suitable for renovations and modifications; and
readily applied as a coating to existing structures and objects.
Embodiments of the present invention can be applied to land, sea, or airborne vehicles or fixed facilities. Incorporating the invention into a design saves capital as well as operations and maintenance costs. Further, a preferred embodiment of the present invention may be used anywhere in the world that common building practices are followed.
Preferred embodiments are fully disclosed below, albeit without placing limitations thereon.